1. Field of the Invention
The present invention relates to an input device suitable for a portable handset, and particularly, but not exclusively, to an input device for a mobile telephone.
2. Description of the Related Art
Mobile telephone technology has evolved to a stage where the size of handsets is limited, in some instances, by the size of the user interface. The user interface can be generally considered to comprise an input device and a display, although the functionality of the input device and the display may be combined.
The input device typically comprises a keypad, which provides keys for entering numbers to facilitate the making of telephone calls, and keys for enabling functions to be selected, such as a function to start a call or end a call for example. A typical mobile telephone keypad may have seventeen keys.
In applications where it is desirable to minimize the size of the mobile telephone, the need to provide a usable input device for the mobile telephone may limit the reduction of the size of the telephone. In very small scale applications, it may not be possible to provide sufficient space for the input device.
Various techniques have been used in the art of mobile telephony to attempt to solve the problems associated with the need to provide the input device. It is known to provide the input device as a keypad comprising an array of very small keys or buttons. However beyond a certain size reduction, such keypads become difficult to use, and it may be difficult to select the depression of an individual key. It has also been known to provide keypads comprising unconventional arrays of keys in combination with the keys themselves being small. However such unconventional arrays of keys can be aesthetically unpleasing, and can also be awkward to use. It has also been proposed to provide voice recognition means as the input device for mobile telephones, and thereby eliminate the need for a keypad or require a keypad with a reduced number of keys. However voice recognition can be unreliable, and requires training. Voice recognition may also often be impractical to use, for example when it is desired to send a text message, such as a short messaging service (SMS) message, during a meeting. Another attempt to provide a reduced size input device on a mobile telephone or a portable device generally has been to provide a touch-pad with a stylus, functioning as a combined input device and display. A touch-pad is limited in use when miniaturised, however, and additional space is also needed to store a stylus. Thus the provision of a touch-pad in itself creates further size problems.